Oil sealed mechanical rotary vacuum pump



Jan. 31, 1967 B. BUCHEL 3,301,474

OIL SEALED MECHANICAL ROTARY VACUUM PUMP Filed Sept. 24. 1965 J ff 1 INVENTOR.

United States Patent 3,301,474 OIL SEALED MECHANICAL ROTARY VACUUM PUMP Baptist Biichel, Balzers, Liechtenstein, assiguor to Bendix Balzers Vacuum, Inc., Rochester, N.Y., a corporation of Delaware Filed Sept. 24, 1965, Ser. No. 489,821 1 Claim. (Cl. 230-205) The present invention relates to oil sealed mechanical vacuum pumps having a channel in the pump casing for the admission of atmospheric air into a working space of the pump during operation.

Such an air inlet can, as is well known, serve different purposes. First, it is necessary to supply the working chamber with air if condensable vapors are to be pumped off. This example has been described in detail in German Patent No. 702,480. The air supply may also be used to soundproof pumps having a discharge valve. The two eifects can, of course, be achieved simultaneously in one pump. In both cases it is essential that a predetermined but not excessive amount of air be supplied to the working chamber of the pump when the chamber is shut ofi from the inlet side of the pump. Therefore, the channel for the air inlet not only has to make it possible for the air to enter but, at the same time, has to act as a restrictor, which is regulated in such a way that just the right amount of air is introduced. The air inlet mechanisms heretofore used were generally valves having adjustable aerodynamic resistance. Such mechanisms have the disadvantage that the valves become easily clogged by invading dust particles because of the small admissasble openin especially when a pump has to be operated in a dusty room. Clogging may also occur through gumming of the valve by the sealing oil, or by obstruction of the valve by foreign bodies which find their way into the pump through the intake. This results in the necessity of frequent cleaning or frequent failure of the air inlet arrangement.

The present invention has as its object the reduction or elimination of clogging of the air inlet system.

According to the present invention the air intake chan nel is, on the one hand, dimensioned and arranged in such a way that it will be able to accommodate the amount of oil discharged from the working chamber during each pump stroke, and is, on the other hand, provided with a restriction which is dimensioned and arranged in the air intake channel in such a way that it will, in the period between every two exhaust strokes, make possible not only the complete return flow to the chamber of the oil washed through the restriction, but also the subsequent supply or the desired amount of air into the working chamber.

Other objects and advantages of the present invention will become readily apparent tfirom the following detailed description taken in connection with the appended drawings in which:

FIGURE 1 is a sectional view of a rotary vacuum pump embodying the invention,

FIGURE 2 shows an enlarged fragmentary view of FIGURE 1,

FIGURE 3 is a view similar to that of FIGURE 2 illustrating another embodiment of the invention.

Referring now to the drawings, numeral 1 designates the casing of a vacuum rotary oil sealed mechanical pump having a rotor 2, vanes 3 and 4', suction port 5, discharge orifice 6, discharge valve 7, and oil bath 8 covering the discharge valve. An air inlet conduit 10 is provided for the feeding of air into the working or discharge chamber 9 of the pump during operation through a passage 11 in pump casing 1 which leads from the working or discharge chamber 9. Conduit 10 is threadedly secured in a bore 12 formed in pump casing 1 in vertical alignment with passage 11. Conduit 10 extends vertically into chamber 13 and terminates above the level of the oil bath 8. The internal diameter and the length of the conduit 10 are dimensioned in such a way that the amount of oil which is ejected through opening 11 with each pump stroke can essentially be taken up through conduit 10. The restriction for the air inlet conduit can be formed in different ways according to the present invention.

FIGURES 1 and 2 show the arrangement of a ball 14 in the air inlet bore 12. Ball 14 is pressed against the lower end of the conduit 10 by spring 15 and would close the end of conduit 10 completely except that port or opening 16 in the wall of the conduit 10 enables the air to bypass ball -14 and enter the pump. As can be seen in the drawing, ball 14 furthermore forms an additional restriction at 17, the area of which is adjustable by screwing conduit 10 more or less deeply into the bore 12. This arrangement is recommended if adjustability of the air supply is desired during operation.

FIGURE 3 illustrates another embodiment of the invention in which a simple disk 18 formed with a suitable bore can be inserted as the restriction. The disk is easily interchangeable so that the air supply can be adapted to the various conditions of operation.

In the device embodying the present invention, the air inlet restriction is washed by oil flowing in both directions through the restriction during each pump cycle whereby the restriction is continuously freed of adhering dirt particles.

The washing or flow through the restriction in both directions has significance in that larger dirt particles which cannot enter through the restriction, can be washed away either in one or the other direction. In the present invention the restriction is located so deeply in the air inlet conduit that part of the oil ejected with each pump stroke is forced through it. Contrary to this, in all previously known pumps having an air inlet restriction, the restriction was so located that it was possible to accommodate all of the oil eject-ed with each pump stroke beneath the restriction. The desirability of continuously washing the air inlet restriction with ejected oil has not been previously disclosed.

I claim:

In an oil sealed vacuum pump having a housing, a rotary pump member in said housing dividing the interior of said housing into a suction chamber and a discharge chamber, an oil bath, means connecting said oil bath to said discharge chamber, and an air inlet system comprising:

a conduit threadedly mounted in a bore in said housing adapted to connect said discharge chamber to a source of air;

restriction means fiormed in said conduit means sufficiently near to said discharge chamber to be washed by the oil discharged from said discharge chamber during each pump cycle;

said restriction means includes a spring loaded ball valve engaging said conduit and having an adjustable position with respect to said bore, said position being controlled by the threaded position of said conduit.

References Cited by the Examiner UNITED STATES PATENTS 2,885,143 5/ 1959 Dubrovin. 3,053,439 9/1962 Brill 230205 3,151,808 10/1964 Saath 23020=5 ROBERT M. WALKER, Primary Examiner. 

